1. Field of the Invention
The present invention relates to a method of cutting a laminate, an apparatus for manufacturing the laminate, a method of manufacturing the laminate, and the laminate itself. In more detail, the present invention relates to a method of cutting a laminate formed of substrates of different types of laminated materials. More particularly, the present invention relates to a method of cutting a laminate formed of substrates of respective materials, the corresponding transmittance or absorptance properties of which, with respect to irradiation by a laser beam, being different from each other.
2. Description of the Related Art
A device comprising a laminate including a plurality of substrates of different types of materials has recently been developed. Highly technical devices, such as micro-electronics-mechanical-system (MEMS) devices, are configured as a laminate of a substrate formed of silicon, and a substrate of lithium tantalate (LiTaO3), sapphire, or heat-resistant glass, etc, superposed together. In fabricating such a device, the laminate composed of a plurality of substrates of different types of materials is cut into separate devices (chips).
In a conventional method, a semiconductor wafer is cut into separate semiconductor chips by rotating a wheel containing diamond abrasive grains at high speed. The wheel containing the diamond abrasive grains can be used also for separating the laminate of a plurality of substrates formed of different types of materials into individual devices.
In fabricating a device having a fine mechanism such as a MEMS device, however, an attempt to separate the laminate into individual devices using the wheel containing diamond abrasive grains poses the problem that the contact between the wheel and the laminate at the time of cutting operation causes the laminate to vibrate and often damages the fine mechanism of the device.
In the case where a device having a fine mechanism such as a MEMS device is fabricated, therefore, some measure is required to prevent the vibration of the laminate, and a cutting method using a laser is one choice. In the cutting method using the laser, however, the material is required to absorb the laser light, and therefore the combinations of the lasers and the materials to be cut are limited.
In the case where the laminate including a plurality of substrates of different types of material is separated into individual devices, therefore, it is necessary to use a plurality of lasers having wavelengths suitable for a plurality of materials, respectively. Japanese Unexamined Patent Publication (Kokai) No. 2003-37218, for example, discloses a method of cutting a multilayer substrate with a dual laser irradiation, in which a first laser is focussed on a first substrate, and a second laser is focussed on a second substrate.
In the case where the laminate including a plurality of substrates of different types of material is separated into individual devices, therefore, as many laser oscillators as there are stacked substrates are required, thereby leading to the problem of an expensive, bulky dicing apparatus.
For cutting a laminate formed of silicon having the thickness of several hundred μm and pyrex glass having the thickness of several hundred μm, such as a MEMS device recently developed, a YAG laser (laser wavelength λ of 1.064 μm) can be used as a laser capable of cutting the silicon efficiently. As a laser capable of cutting glass, on the other hand, an ultraviolet laser (laser wavelength λ of 0.35 μm) typically including the excimer laser and the THG-YAG laser or an infrared laser (laser wavelength λ of 5 μm or more) typically including the CO2 laser are available. The ultraviolet laser, however, requires a long time for cutting, and for example, several hours or longer to cut one line of 100 mm. The use of the infrared laser, on the other hand, results in the laser irradiation width of at least 1 mm in the cutting operation, and adversely affects the internal circuits in an application to a small device.
In the case where a member, in which a silicon member and glass member are joined to each other, is cut, the following problems are encountered.
First, in the case where the silicon member side is irradiated with a laser beam so as to conduct laser beam machining, as the laser beam is absorbed by the silicon layer, it is possible to cut the silicon layer. However, the glass member transmits the laser beam. Therefore, cutting is stopped on the joining face on which the glass member and the silicon member are joined to each other.
On the other hand, in the case where the glass member side is irradiated with a laser beam, the laser beam penetrates the glass member and reaches the silicon face. In this case, as the silicon member is cut, the glass member can be machined while being penetrated by the laser beam. However, a problem is caused in that cracks are generated on the joining interface of the glass member and the silicon member.